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to maps, both geographical and geological, to which no space could be allotted in an elementary handbook. But there is one rich district which seems to require special notice here in order to remove what seems to be a prevalent misconception. In the body of the present handbook frequent references are made to the occurrence of many gem-stones in Ceylon. The search for these beautiful minerals and the traffic in them has, in fact, been going on in that island for ages, while the plumbago and mica industries are affairs of to-day. Yet it is strange that the importance of the Ceylon trade in precious stones remains unrecognised not only in newspaper correspondence but in official documents and in standard looks. One meets with such a statement as this—"Plumbago is, practically, our only mineral export"; and this, "The yield of gems in this island is not large, the total value of the annual production being said to be no more than ₤10,000." A glance at the true figures suffices to demonstrate the incorrectness of such statements. The value of plumbago exported from Ceylon in 1903 amounted to ₤119,316. Now the value of the gems exported in an average recent year by a single Colombo merchant was ₤30,000, while there are a score of other Ceylon gem merchants who together export no less than ₤200,000 worth annually. With casual sales to visitors to the island and to travelling dealers, a moderate estimate of the annual export of gems from Ceylon will be ₤300,000. The variety of kinds found is large, sapphires, spinels, alexandrites, chrysoberyls, beryls, topazes, catseyes, tourmalines, zircons, garnets and moonstones being the chief: diamonds, emeralds and turquoises do not occur, while pearls belong to a different category, being organic products. But it must be allowed that the precious stone industry constitutes now, as it has done for many centuries, an important feature in the resources of the island.

In concluding these prefatory notes I have much pleasure in acknowledging the help of Dr. C. A . MacMunn, to whose skill in spectroscopy many scientists are largely indebted. He drew for me the absorption-spectra of almandine and of zircon, reproduced in the coloured frontispiece. Although more exact in details, these drawings do not, I am glad